The present invention is directed to receiver devices, and especially to telecommunication receiver devices. Receiver devices are commonly designed to receive signals at a predetermined carrier frequency. However, environmental and other influences can operate to somewhat alter the parameters of a received signal at a receiver device. For example, a carrier signal for an optical fiber telecommunication system may be designed at 2.5 GHz (gigahertz), but fiber cables can stretch or shrink because of temperature fluctuations so that a sort of Doppler effect can alter the phase of signals from the designed carrier signal as they arrive at a receiver device. As a consequence, receiver devices are often provided with a capability for noting certain characteristics of arriving signals in order to enable accurate interpretation of the received signals. Thus, receiver devices are often capable of ascertaining such signal characteristics as zero-crossings, leading edges, trailing edges or combinations of such characteristics. Such a capability permits a receiver device to ascertain a “receiver clock” periodicity for received signals. Accurately ascertaining the “receiver clock” for a received signal assures that the receiver device can properly interpret digital information conveyed in the received signal, accurately ascertaining how long a “1” lasts or a “0” lasts, and interpreting where “edges” occurs in the signaling.
Industry standards have become important in various technology areas to ensure that various manufacturers can produce products that are compatible with each other in the marketplace. This trend is beneficial to consumers in that it permits purchasing equipment form a variety of manufacturers without being limited to the technology of a particular producer. Telecommunications is a technology area that has experienced a significant degree of standards activity, including, by way of example, fiber optic telecommunication networks.
A prevalent standard for fiber optic telecommunications is the SONET (Synchronous Optical NETwork) standard. Among the parameters specified in the SONET standard are specifications regarding the telecommunication system's handling of jitter. Jitter is a manifestation of phase shift of digital pulses over a transmission medium, such as a fiber optic cable. As mentioned earlier herein, temperature fluctuations can operate to stretch or shrink optical cables so that the phase of signals is altered as they traverse the optical cable, thereby introducing jitter.
There are typically three measures of how well a telecommunication system handles jitter: (1) jitter generation—how much jitter a device or system generates when it is provided with a signal having zero jitter; (2) jitter transfer—when a data stream with a known amount of jitter is input to a device or system, how much jitter is present in data coming out of the device or system; and (3) jitter tolerance—how much jitter can an incoming data stream have before a device or system starts to “drop bits” (i.e., starts to misread data conveyed by the signal).
Jitter generation involves providing a quiet, accurate clock for a device or system. Jitter transfer involves providing a lower bandwidth for a device or system in order to reject noise. A practical consequence of such a lower bandwidth is that the device or system counts bits in received signals more slowly. Jitter tolerance involves providing a higher bandwidth for a device or system in order that the device or system can react more quickly to recognize and accommodate phase shifts in received signals. Thus, in order to meet established standards for a system (e.g., a SONET standard), one must set bandwidth low enough to meet jitter transfer standards while ensuring that bandwidth is high enough to meet the jitter tolerance specification; the two aspects of jitter accommodation (i.e., jitter transfer and jitter tolerance) require conflicting remedies, conflicting bandwidth requirements.
Ensuring jitter tolerance is sufficient to provide continuity of communications in a device or system is an important design aspect for a receiver device or system. It often occurs that one must adjust operating parameters of a device or system (e.g., bandwidth) temporarily out of compliance with a standard in order to provide the desired continuity of communications. One solution would be to provide a manual selection switch for a user of a device or system to select a higher or lower bandwidth as jitter tolerance must be altered to accommodate extant received signals. However, such a manual bandwidth selecting capability would be cumbersome and unreliable to operate.
There is a need for an automatic apparatus and method for dynamically adjusting bandwidth of a receiver device or system for automatically adjusting jitter tolerance of the receiver device or system.